Cyclosporine A promotes renal fibrosis through activating endoplasmic reticulum stress by targeting miR-212-5p/ATF6 axis

INTRODUCTION: Cyclosporine A (CsA) is a widely used immunosuppressive drug, but its long-term use is associated with renal fibrosis. Despite its clinical importance, the molecular mechanisms underlying CsA-induced renal fibrosis remain poorly understood. METHODS: We used C57BL/6 mice (n = 6 per group) treated with CsA (30 mg/kg/day, gavage) and Boston University mouse proximal tubular (BUMPT) cells (n = 6 per group) exposed to CsA (8 µM). Assessments included Masson's trichrome staining, Western blot, quantitative real-time PCR, immunohistochemistry, and in situ hybridization. Mechanistic studies employed miR-212-5p mimics and inhibitors, activating transcription factor 6 (ATF6) overexpression, and the endoplasmic reticulum (ER) stress inhibitor 4-phenylbutyric acid (4-PBA). Data are presented as mean ± standard deviation; statistical significance was defined as p < 0.05. RESULTS: CsA induced significant renal fibrosis in vivo and in vitro, evidenced by increased collagen deposition and elevated expression of alpha-smooth muscle actin (α-SMA), fibronectin, collagen type I and IV, and key profibrotic factors (p < 0.05). RNA analysis revealed that miR-212-5p was markedly upregulated in CsA-treated kidneys, predominantly in renal tubules. Concurrently, ATF6, a protective component of the unfolded protein response (UPR), was significantly downregulated. Bioinformatics prediction and luciferase reporter assays confirmed that miR-212-5p directly targets the 3' untranslated region of Atf6 mRNA. Functionally, miR-212-5p mimic exacerbated CsA-induced ATF6 suppression and fibrosis, whereas anti-miR-212-5p restored ATF6 expression, attenuated ER stress, and significantly reduced fibrotic markers. Similarly, ATF6 overexpression or ER stress inhibition with 4-PBA ameliorated CsA-induced fibrosis. CONCLUSIONS: Our findings position miR-212-5p as a previously unrecognized molecular target of CsA and establish the miR-212-5p/ATF6 axis as a central driver of CsA-induced nephrotoxicity. The findings provide new insights into the molecular mechanisms of CsA nephrotoxicity and identify a potential therapeutic target for preventing CsA-induced renal fibrosis.